This invention relates to a miniaturized, programmable radiation source having an x-ray emitting probe for use in delivering substantially constant or intermittent levels of x-rays to a specified region and, more particularly, to a biocompatible sheath, for covering the probe during treatment, or a biocompatible sheath and probe treatment kit.
In the field of medicine, radiation is used for diagnostic, therapeutic and palliative treatment of patients. The conventional medical radiation sources used for these treatments include large fixed position machines as well as small, transportable radiation generating probes. The current state of the art treatment systems utilize computers to generate complex treatment plans for treating complex geometric volumes.
Typically, these systems apply doses of radiation in order to inhibit the growth of new tissue because it is known that radiation affects dividing cells more than the mature cells found in non-growing tissue. Thus, the regrowth of cancerous tissue in the site of an excised tumor can be treated with radiation to prevent the recurrence of cancer. Alternatively, radiation can be applied to other areas of the body to inhibit tissue growth, for example the growth of new blood vessels inside the eye that can cause macular degeneration.
Conventional radiation treatments systems, such as the LINAC used for medical treatment, utilize a high power remote radiation source and direct a beam of radiation at a target area, such as tumor inside the body of a patient. This type of treatment is referred to as teletherapy because the radiation source is located at a predefined distance, typically on the order of one meter, from the target. This treatment suffers from the disadvantage that tissue disposed between the radiation source and the target is exposed to radiation.
An alternative treatment system utilizing a point source of radiation is disclosed in U.S. Pat. No. 5,153,900 ('900 patent) issued to Nomikos et al., owned by the assignee of the present application, which is hereby incorporated by reference. As shown in FIG. 1, the system 10 includes an x-ray source 12 and a miniaturized insertable probe assembly 14 capable of producing low power radiation in predefined dose geometries or profiles disposed about a predetermined location. The probe assembly 14 includes a shoulder 16 which provides a rigid surface by which the system 10 may be secured to another element, such as a stereotactic frame used in the treatment of brain tumors. The probe assembly 14 also includes an X-ray emitting tube 18, or "probe", rigidly secured to shoulder 16. This type of treatment is referred to as brachytherapy because the X-ray source is located close to or in some cases within the area receiving treatment. One advantage of brachytherapy is that the radiation is applied primarily to treat a predefined tissue volume, without significantly affecting the tissue in adjacent volumes.
Typical radiation therapy treatment involves positioning the insertable probe 18 into the tumor or the site where the tumor or a portion of the tumor was removed to treat the tissue adjacent to the site with a "local boost" of radiation. In order to facilitate controlled treatment of the site, it is desirable to support the tissue portions to be treated at a predefined distance from the radiation source. Alternatively, where the treatment involves the treatment of surface tissue or the surface of an organ, it is desirable to control the shape of the surface as well as the shape of the radiation field applied to the surface.
The treatment can involve the application of radiation, either continuously or intermittently, over an extended period of time. Therefore, in some cases, the insertable probe 18 is adjustably supported in a compliant manner to accurately position the radiation source with respect to the treated site and accommodate normal minor movements of the patient, such as movements associated with breathing.
It is typically considered essential that the interface between the patient and the probe 18 be biocompatible. However, the probes are not always made from such material. Rather, as disclosed in the '900 patent and shown in probe assembly 14 of FIG. 2A, the probe 18 is usually a hollow, evacuated cylinder made of a beryllium (Be) cap 24 at one end, a molybdenum-rhenium (Mo--Re), molybdenum (Mo) or mu-metal tubular body 22 , and a probe shoulder 16 opposite the Be cap 24. The tubular body 22 is rigidly secured to the probe shoulder 16 using bushing element 20. A target assembly 26 is located inside the Be Cap 24 of probe 18 and emits x-rays in response to an incident electron beam produced from the x-ray source 12 of FIG. 1. The target assembly includes an x-ray emission element consisting, typically, of a small beryllium (Be) target element 26 located within the cap 24 and coated on side exposed to the incident electron beam with a thin film or layer of a high-Z element, such as tungsten (W), uranium (U) or gold (Au). A typical probe of this type is 10-16 cm in length and has an inner diameter of about 2 mm and an outer diameter of about 3 mm.
Probe 18 is comprised of materials which maximize the x-ray emitting characteristics of the device, rather than materials which concern themselves with biocompatibility. Therefore, a biocompatible sheath 50, shown in FIG. 2B, is typically used to encase the probe 18 during patient treatments. Such sheaths 50 are usually comprised of an elongated and cylindrical (assuming the probe to be cylindrical) body 52, very closely mimicking the dimensions of the probe 18. Additionally, a sheath 50 has a smooth hollow interior cavity defined by an inner surface of the sheath body 52 and a closed end 58 of the sheath 50. The diameter of the inner surface of the sheath is about 3.3 mm, and accommodates insertion of a probe having an outer diameter of about 3 mm, as described above. Opposite the closed end 58, is an open end 56, which accommodates insertion of the probe 18 within the sheath 50. Near the open end 56 of the sheath is a flange 54 and an annular ring 62, as shown in FIG. 2C. The circumferential outer surface of annular ring 62 is integral with the inner surface of sheath 50 and oriented within or near flange 54. The probe opening formed within annular ring 62 is about 2.9 mm, which accommodates insertion of a probe body 22 of diameter of about 3 mm into the sheath 50, in the direction of arrow 30. Annular ring 62 ultimately comes to rest, at the terminus of the probe's 18 insertion into the sheath 50, near the probe shoulder 16, thereby removably securing the sheath 50 to the probe 18. Because the diameter of the annular ring is less than the diameter of the probe body 22, annular ring 62 is made to be compliant relative to probe body 22. The compliance of the annular ring 62 causes the sheath 50 to securely grip probe 18, so that sheath 50 does not become easily removed from the probe 18 during use. To achieve the desired advantages of biocompatibility and a compressible securing assembly, sheath 50 is typically made out of an aliphatic thermoplastic material, for example, "Tecoflex.RTM." (supplied by Thermedics Inc. of Waltham, Mass.).
A problem with typical sheaths is that as a result of the smaller inner diameter of annular ring 62, relative to the probe's outer diameter, and the location of the ring 62 at or near flange 54 of the sheath 50, air becomes trapped within the region between the sheath 50 and probe 18, as the probe 18 is inserted into the sheath 50, as shown in FIG. 2C. Therefore, it can be difficult to insert the probe within the sheath without exerting an undesirable amount of force on the probe and sheath combination, which could lead to bending of the probe. Additionally, there is an inability to fully seat the sheath on the probe due to the gas pressure at the closed end of the sheath which dislodges the sheath from the probe.
It is an object of the present invention to provide an X-ray treatment kit which includes a probe and sheath combination for use with an X-ray treatment apparatus, the combination allowing the escape of air existing between the probe and the sheath during insertion of the probe into the sheath.
It is a further object of the present invention to provide an improved sheath to be used with typical smooth probes, wherein the sheath provides an airflow path for the escape of air present between the probe and sheath during insertion of the probe into the sheath.